Start with your smaller 12 pixel ring.  Solder a red wire to 5v, a black wire to G, and a white wire to Data IN.  It's easiest to insert the wires from the front and solder on the back of the ring.

Trim the wires to about 1/2" and strip the ends.  Twist another red wire and another black wire together with the wires you soldered. 

Place the 12 pixel ring on top of the 16 pixel ring.  Solder BOTH the twisted red and black wires into the respective 5v and G holes on the second ring. 

Solder the white wire coming from the smaller ring into the Data OUT pin.  Then, add another wire to the 16 pixel ring's Data IN pin.

Pull the three loose wires through so they come out the back of the larger ring.  Trim the wires and solder them to the Gemma: red to Vout, black to GND, and your data wire to D1.

Solder a 2" wire to gemma's pin D0.  This wire will connect Gemma's capacitive touch pad to your metal pendant front to activate the capacitive touch features.

Set the battery inside the large ring and nestle it against the back of the smaller ring.  Center the rings so the LEDs show as much as possible. 

Place the Gemma on the back of the pile, with the switch facing up.  Be sure the battery wire can be pulled out easily and replaced -- you'll need to unplug this for charging.  Once it's all aligned, glue all the components together with E6000 glue or epoxy.

Thread the capacitive touch wire UNDER the battery wires if needed.  Trim the wire and strip and tin the end.  Solder it securely to the back of your metal pendant.  Add a blob of glue on top of the solder to keep it secure.

Add a necklace cord.  Put your pendant on, above your bare skin (not over a shirt or sweater) and touch to change color modes.  

You may need to do some calibration in the code to get it reacting correctly to your touch.